1. Field of the Invention
The present invention relates to a viscous fluid coupling suitable for an automobile machinery such as, a cooling fan or the like.
2. Description of the Prior Art
A conventional viscous fluid coupling is disclosed in the specification of, for instance, Japanese Patent Laid-Open No. 69336/1980. This type of coupling will be explained with reference to FIG. 3. A rotor 1 is fixed to an input shaft 2. Operation chambers 5a, 5b are formed between a case 3 and a cover 4 (an output shaft) fixed to the case 3. The operation chambers 5a, 5b are filled with viscous fluid, whereby torque is propagated from the input shaft 2 to the output shaft. The reference numeral 6 stands for a storage chamber, 7 represents a temperature sensitive member and 8 denotes a rod. The temperature sensitive member 7 is linked through the rod 8 to a valve 9. This valve 9 opens and closes through the intermediary of the rod 8 in response to a temperature that the sensitive member 7 senses. Propagation of torque from the input shaft 2 to the output shaft is controlled by regulating the viscous fluid pumped between the operation chambers 5a, 5b and the storage chamber 6.
There is, however, a defect in the viscous fluid coupling depicted in FIG. 3. The viscous fluid becomes stagnant in the lower portion of the coupling by reason of no power during non-operational a period, so that that viscous fluid, as shown in FIG. 4, fills the operation chambers 5a, 5b as well as the storage chamber 6. The torque is propagated from the input-side by the viscous fluid with which the operation chambers 5a, 5b are filled when the operation resumes. The fan continues to rotate undesirably at a high velocity till the viscous fluid is pumped from the operation chambers 5a, 5b into the storage chamber 6.
In such a case, if the atmosphere is adequately high in temperature and the valve is thus kept open, no problem is produced. However, if the atmosphere is at a low temperature, there arise problems such as deterioration both in warming-up speed of the machinery and in the efficiency of a heater, or the creation of noises caused by the fan immediately after restarting the operation.
A conventional viscous fluid coupling has been proposed in the specification of Japanese Patent Laid-Open No. 190521/1984 to obviate the above-described defects. Such is the arrangement that a plurality of floats are provided in the storage chamber; each individual float is subjected to a force given by an elastic member and is positioned towards the axial center of the storage chamber while the engine stops; and the floats move to the outer periphery of the storage chamber by centrifugal forces created by rotation of an output member, resisting the force given by the elastic member. With this arrangement, a so-called taking-around phenomenon that is present when the engine starts can be eliminated. In this case, however, the components increase in number and hence the structure become complicated with a heavier weight. Consequently, the costs of production go up.